Superjunction structure, superjunction MOS transistor and manufacturing method thereof

ABSTRACT

A superjunction structure with unevenly doped P-type pillars ( 4 ) and N-type pillars ( 2   a ) is disclosed. The N-type pillars ( 2   a ) have uneven impurity concentrations in the vertical direction and the P-type pillars ( 4 ) have two or more impurity concentrations distributed both in the vertical and lateral directions to ensure that the total quantity of P-type impurities in the P-type pillars ( 4 ) close to the substrate ( 8 ) is less than that of N-type impurities in the N-type pillars close to the substrate; the total quantity of P-type impurities in the P-type pillars close to the top of the device is greater than that of N-type impurities in the N-type pillars close to the top. A superjunction MOS transistor and manufacturing method of the same are also disclosed. The superjunction structure can improve the capability of sustaining current-surge of a device without affecting or may even reduce the on-resistance of the device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Chinese patent applicationnumber 201110295521.0, filed on Sep. 30, 2011, the entire contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a power semiconductor device, and moreparticularly, to a superjunction semiconductor device.

BACKGROUND ART

Superjunction structure is a structure composed of alternately arrangedN-type pillars and P-type pillars. A superjunction MOS transistor isformed by replacing the N-drift region of a VDMOS (VerticalDouble-diffused MOSFET) device with a superjunction structure. By usinga low-resistivity epitaxial layer, a superjunction MOS transistor mayachieve a much lower on-resistance than a conventional VDMOS devicewhile maintaining the same reverse breakdown voltage.

The distribution of N-type impurities in the N-type pillars, thedistribution of P-type impurities in the P-type pillars, and thematching between the distributions of N-type and P-type impurities inthe alternately arranged N-type and P-type pillars in a superjunctionstructure will affect the properties of the superjunction semiconductordevice, including its reverse breakdown voltage and current handlingcapacity.

Generally, the alternately arranged N-type pillars and P-type pillars ina superjunction semiconductor device adopts a design of optimizedelectric charge balance so as to obtain a maximum reverse breakdownvoltage, but in such devices, the current handling capacity isinsufficient.

One method to improve the current handling capacity is to have thedoping concentrations of P-type impurities in the P-type pillars in asuperjunction structure unevenly distributed in the directionperpendicular to the surface of the substrate (i.e. in the verticaldirection), while keeping the doping concentrations of N-type impuritiesin the N-type pillars evenly distributed. If the widths of the P-typeand N-type pillars are equal to each other, then have the concentrationof P-type impurities in the upper part of the P-type pillars higher thanthe concentration of N-type impurities in the N-type pillars, and havethe concentration of P-type impurities in the lower part of the P-typepillars lower than the concentration of N-type impurities in the N-typepillars. Based on the above method, Infineon Technologies proposed adetailed solution to divide each P-type pillar in the superjunctionstructure into six sections along the vertical direction, and let theconcentrations of P-type impurities in the six sections from the topdown be respectively 30%, 20%, 10%, 0%, −10% and −20% higher than theconcentration of P-type impurities in an optimized electric chargebalance.

Currently, manufacturing methods of superjunction structure in asuperjunction semiconductor device can be overall classified into twotypes. The first type is to either form an epitaxial layer of one dopingtype with a certain thickness and then perform lithography and ionimplantation in certain regions of the epitaxial layer to form pillarsof another doping type, or form an undoped epitaxial layer with acertain thickness, and then perform lithography and ion implantation toform N-type and P-type pillars in the epitaxial layer; the above step isrepeated for a few times to form N-type and P-type pillars with adesired thickness. The second type is to etch trenches in a region ofone doping type, and then perform trench filling, or epitaxy or ionimplantation to the trenches to form pillars of another doping type forone-time.

The above described superjunction structure with improved currenthandling capacity requires a variation in the impurity concentrationsdistributed in the P-type pillars. But depending on the existing art,the method of the second type is impractical, and the method of thefirst type has shortcomings of high process costs, long manufacturingtime and great difficulty in production control.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a new type ofsuperjunction structure to improve the capability of sustainingcurrent-surge during the turn-off transient of a device withoutaffecting the reverse breakdown voltage of the device. A manufacturingmethod of the superjunction structure is also provided.

To achieve the aforementioned objective, the present invention providesa superjunction structure, which includes an N-type epitaxial layer anda plurality of P-type pillars formed in the N-type epitaxial layer; apart of the N-type epitaxial layer between each two adjacent P-typepillars serves as an N-type pillar, so as to form alternately arrangedP-type pillars and N-type pillars in the N-type epitaxial layer;

each P-type pillar is unevenly doped both in vertical and lateraldirections; a doping concentration in a lower portion of the P-typepillar is less than or equal to a doping concentration in an upperportion of the P-type pillar;

each N-type pillar is unevenly doped in the vertical direction; a dopingconcentration in a lower portion of the N-type pillar is greater than orequal to a doping concentration in an upper portion of the N-typepillar;

in a bottom of the superjunction structure, a total quantity of P-typeimpurities in P-type pillars is less than a total quantity of the N-typeimpurities in the N-type pillars;

in a top of the superjunction structure, a total quantity of P-typeimpurities in P-type pillars is greater than a total quantity of N-typeimpurities in the N-type pillars.

The superjunction structure of the present invention can also beachieved by changing all the above elements to reverse doping types.

Each P-type pillar is unevenly doped both in vertical and lateraldirections, for example, by such structure: each P-type pillar includesat least two sections in the vertical direction, wherein a secondsection from the top down has a groove formed in its top; the groove hasa profile wider at the top and narrower at the bottom; a first sectionfrom the top down is formed in the groove and also has a shape wider atthe top and narrower at the bottom; each section of a P-type pillar isevenly doped, and the doping concentrations in the respective sectionsof a P-type pillar decrease from the top down.

The present invention further provides a manufacturing method of thesuperjunction structure. The method includes the following steps:

step 1: form a plurality of trenches in an N-type epitaxial layer bylithography and etch; a part of the N-type epitaxial layer between eachtwo adjacent trenches serves as an N-type pillar;

step 2: fill the trenches with a P-type silicon by conducting at leasttwo filing steps from the bottom up; a latter filing step adopts agreater doping concentration of the P-type silicon than a former filingstep, wherein the P-type silicon filled by the second last filing stepin each trench has a groove formed in its top; the groove has a profilewider at the top and narrower at the bottom; the P-type silicon filledby the last filing step in each trench is formed in the groove formed bythe second last filing step;

step 3: remove the P-type silicon above a surface of the N-typeepitaxial layer; the remaining P-type silicon filled by the last filingstep in each trench serves as the first section (top section) of theP-type pillar, and the remaining P-type silicon filled by the secondlast filing step serves as the second section of the P-type pillar fromthe top down.

Take the embodiments of the present invention as example, thesuperjunction structure of the present invention has such features thatthe impurity distributions in the P-type and N-type pillars are bothuneven, wherein the impurity distributions in the N-type pillars areuneven in the vertical direction; the impurity distributions in theP-type pillars adopt two or more doping concentrations both in thevertical and in the lateral directions to ensure that the totalquantities of P-type impurities in the part of the P-type pillars closeto the N-type heavily doped substrate (i.e., the bottom of thesuperjunction structure) is less than the total quantity of N-typeimpurities in the part of the N-type pillars close to the substrate,while the total quantity of P-type impurities in the part of the P-typepillars close to the top of the device (i.e., the top of thesuperjunction structure) is greater than the total quantity of N-typeimpurities in the part of the N-type pillars close to the top.

As the total quantity of P-type impurities is greater than that ofN-type impurities in the top region of the device, the capability ofsustaining current-surge of the device during the turn-off transient canbe improved.

As the P-type pillars are unevenly doped both in the vertical andlateral directions, the regional electric fields in the P-type pillarsbecome stronger, so that the breakdown of the device will occur in theP-type pillars, thus improving the stability of the capability ofsustaining current-surge of the device.

As the part of the P-type pillars close to the N-type heavily dopedsubstrate has a doping concentration no greater than the dopingconcentration when the P-type pillars are evenly doped, theon-resistance of the device will not be affected, or may even bereduced.

The manufacturing method of the superjunction structure also has theadvantages of short processing cycle and low production costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of the superjunction MOS transistoraccording to an embodiment of the present invention;

FIG. 2 a to FIG. 2 d are cross sectional views of the superjunctionstructure in the respective steps of the manufacturing method accordingto an embodiment of the present invention;

FIG. 3 a to FIG. 3 f are schematic views of the relationship betweendoping concentrations in P-type pillars and in N-type pillars of thesuperjunction structure according to embodiments of the presentinvention;

FIG. 4( a) to FIG. 4( h) and FIG. 5( a) to FIG. 5( c) illustrate variousimplementations of the P-type pillars of the superjunction structure ofthe present invention.

DETAILED DESCRIPTION

FIG. 1 is a superjunction MOS transistor employing the superjunctionstructure according to an embodiment of the present invention. Thesuperjunction MOS transistor includes a heavily doped N-type substrate 1and an N-type epitaxial layer 2 formed thereon; a plurality of P-typepillars 4 are formed in the N-type epitaxial layer 2, and a part of theN-type epitaxial layer 2 between each two adjacent P-type pillars 4serves as an N-type pillar 2 a, so as to form alternately arrangedP-type pillars 4 and N-type pillars 2 a in the N-type epitaxial layer 2,namely forming a superjunction structure.

As FIG. 1 illustrates a cross sectional view of a wafer, the P-typepillars 4 and the N-type pillars 2 a all seem to have a rectangularshape. However, in a three-dimensional view, the P-type pillars 4 andthe N-type pillars 2 a may extend in a direction perpendicular to therectangular cross sections for a relatively long distance and formwall-like shapes; or the P-type pillars 4 and the N-type pillars 2 a mayextend in a direction perpendicular to the rectangular cross sectionsfor a relatively short distance and form pillar-like shapes. In theimplementation of wall-like shapes, the overall shape of a P-type pillar4 or an N-type pillar 2 a is approximately rectangular parallelepipedshaped, and may have chamfering structures or arc structures at theedges. In the implementation of pillar-like shapes, the horizontal crosssection of a P-type pillar 4 or an N-type pillar 2 a may have a shape ofa polygon such as rectangle, square, hexagon and octagon.

Each P-type pillar 4 includes two parts: a main body 4 a and anadditional structure 4 b; both the P-type pillar 4 and its main body 4 ahave a height of h1+h2′. A groove is formed in the top of the main body4 a and has a profile wider at the top and narrower at the bottom; adistance between the bottom of the groove and the bottom of the P-typepillar 4 h1 is, for example, from 25 μm to 30 μm. The additionalstructure 4 b is formed in the groove on the top of the main body 4 aand completely fills the groove, and therefore the additional structure4 b also has a profile wider at the top and narrower at the bottom. Theheight of the additional structure 4 b h2′ is, for example, from 2 μm to8 nm. The main body 4 a and the additional structure 4 b are combined toform a rectangular profile.

FIG. 4( a) to FIG. 4( h) illustrate various implementations of the mainbody 4 a and the additional structure 4 b. The profile wider at the topand narrower at the bottom may be V-shaped (FIG. 4( a)),trapezoid-shaped (FIG. 4( b)), funnel-shaped (FIG. 4( c)), or in othershapes.

Each N-type pillar 2 a is unevenly doped, and a doping concentration ina lower portion of the N-type pillar 2 a is always greater than or equalto a doping concentration in an upper portion of the N-type pillar 2 a,namely, the doping concentration in the N-type pillar 2 a is greatest atthe bottom and lowest at the top. In each P-type pillar 4, both the mainbody 4 a and the additional structure 4 b are evenly doped and thedoping concentration of the main body 4 a is lower than the dopingconcentration of the additional structure 4 b. In the bottom of theP-type pillars 4 (i.e., the region close to the N-type heavily dopedsubstrate 1), a total quantity of P-type impurities in a P-type pillar 4is less than a total quantity of N-type impurities in an N-type pillar 2a; in the top of the P-type pillars 4, a total quantity of P-typeimpurities in a P-type pillar 4 is greater than a total quantity ofN-type impurities in an N-type pillar 2 a.

In a preferred embodiment, in each P-type pillar 4, the dopingconcentration of the main body 4 a is lower than or equal to an evendoping concentration of the P-type pillar 4 and the doping concentrationof the additional structure 4 b is greater than or equal to 3 times ofthe even doping concentration of the P-type pillar 4, wherein the evendoping concentration of the P-type pillar 4 is defined as the dopingconcentration of the P-type pillar 4 when the P-type pillars 4 areevenly doped and the total quantity of the P-type impurities in a P-typepillar 4 is equal to the total quantity of the N-type impurities in anN-type pillar 2 a. For example, in each P-type pillar 4, the dopingconcentration of the main body 4 a may be 0.5˜1 time of the even dopingconcentration of the P-type pillar 4, and the doping concentration ofthe additional structure 4 b may be 3˜10 times of the even dopingconcentration of the P-type pillar 4.

In addition to the above new type of superjunction structure, FIG. 1further includes some other structures of a conventional VDMOS device.For example, there is a bowl-shaped gate oxide layer 5 in contact withthe top of each N-type pillar 2 a; each gate oxide layer 5 surrounds apolysilicon gate 6. A P-well 7 is formed corresponding to each P-typepillar 4 and is in contact with the top of the P-type pillar 4 and partsof the tops of the N-type pillars 2 a adjacent to the P-type pillar 4.N-type heavily doped source regions 8 and P-type heavily doped contactregions 11 are formed within the P-wells 7. A dielectric layer 9 isformed above the gate oxide layers 5 and the polysilicon gates 6.Contact hole electrodes 10 are formed above the N-type heavily dopedsource regions 8 and the P-type heavily doped contact regions 11. Asurface metal layer 12 is formed on the dielectric layer 9 and thecontact hole electrodes 10. A source electrode 21 is picked up from thesurface metal layer 12. Gate electrodes 22 are picked up from thepolysilicon gates 6. A backside metal layer 13 is formed on a backsideof the N-type heavily doped substrate 1, and a drain electrode 23 ispicked up from the backside metal layer 13. All the above elements inFIG. 1 form an entire superjunction MOS transistor.

Obviously, it will be still practicable that all the above elements inFIG. 1 are formed with reverse doping types (N-type replaced by P-type,while P-type replaced by N-type).

One objective of the present invention is to provide a new type ofsuperjunction structure. Although FIG. 1 only illustrates an embodimentapplying the new type of superjunction structure to a superjunction MOStransistor, the new type of superjunction structure can also be appliedto other superjunction semiconductor devices, such as IGBT(insulated-gate bipolar transistor), diodes, and so on.

A manufacturing method of the superjunction structure of the presentinvention will be described in details below. Take a superjunction MOStransistor employing the superjunction structure in FIG. 1 for example,the manufacturing method includes the following steps:

Step 1: form an N-type epitaxial layer 2 on an N-type heavily dopedsubstrate 1 by epitaxial growth. The N-type epitaxial layer 2 isunevenly doped and has a thickness of, for example, 45 μm. A dopingconcentration in a lower portion of the N-type epitaxial layer 2 isalways greater than or equal to a doping concentration in an upperportion of the N-type epitaxial layer 2, which can be achieved byepitaxy process. Existing epitaxy equipments are already capable ofgrowing epitaxial layers with variable (can be defined according toneeds) doping concentrations.

Step 2: referring to FIG. 2 a, form a plurality of trenches 3 in theN-type epitaxial layer 2 by lithography and etch for forming P-typepillars 4 in subsequent steps, wherein the trenches 3 have a width of,for example, 4 μm. A part of the N-type epitaxial layer 2 between eachtwo adjacent trenches 3 serves as an N-type pillar 2 a, and the N-typepillars 2 a have a width of, for example, 4 μm.

Generally, a dielectric layer (e.g. silicon dioxide) with a thickness offrom 300 Å to 500 Å may further be deposited on the N-type epitaxiallayer 2, and will become a dielectric layer 9 a after lithography andetch.

Step 3: referring to FIG. 2 b, fill each trench 3 with a P-typemonocrystalline silicon to form first trench filling layers 4 a′,wherein, the height of the first filling layers 4 a′ h is equal to thesum of the heights of the N-type epitaxial layer 2 and the dielectriclayer 9 a. The P-type monocrystalline silicon filled in each trench hasa groove 30 formed in its top. The groove 30 has a profile wider at thetop and narrower at the bottom. A distance between the bottom of thegroove 30 and the bottom of the respective trench 3 is h1. The groove 30may have any one of the shapes shown in FIG. 4( a) to FIG. 4( h). Thefirst trench filling layers 4 a′ are embryonic forms of the main bodies4 a to be formed in subsequent steps.

Step 4: referring to FIG. 2 c, fill P-type monocrystalline silicon witha greater doping concentration than step 3 into the grooves 30 in thetops of the first trench filling layers 4 a′ to form second trenchfilling layers 4 b′ in the grooves 30. The second trench filling layers4 b′ are embryonic forms of the additional structures 4 b to be formedin subsequent steps.

The above step 3 and step 4 may be implemented by epitaxial growth. Theexisting processes are capable of forming groove structures in the topof the first trench filling layers 4 a′.

Step 5: referring to FIG. 2 d, remove the parts of the first trenchfilling layers 4 a′ and the parts of the second trench filling layers 4b′ above the surface of the N-type epitaxial layer 2. This step may beconducted by, for example, chemical mechanical polishing (CMP) or dryetch (etch back) process to polish or etch the silicon in the trenchesuntil the surface of the N-type epitaxial layer 2 is reached. It is alsopractical to polish or etch the silicon in the trenches until a certaindepth below the surface of the N-type epitaxial layer 2 is reached, andthe maximum depth is, for example, less than 3000 Å. The remaining firsttrench filling layer 4 a′ in each trench forms a main body 4 a of theP-type pillar, and the remaining second trench filling layer 4 b′ ineach trench forms an additional structure 4 b of the P-type pillar,wherein the additional structure 4 b has a height of h2.

If there is a dielectric layer 9 a formed on the N-type epitaxial layer2, it should be entirely removed by dry etch or wet etch after thepolishing or etching back process.

The distance between the bottom of the main body 4 a and the bottom ofthe groove h1 may be, for example, 25 μm to 30 μm. The height of theadditional structure 4 b h2 may be, for example, 5 μm to 10 μm. Theheights of the P-type pillar 4, the main body 4 a and the N-type pillar2 a are all h1+h2.

The manufacturing method of the superjunction structure of the presentinvention has been described in the above step 2 to step 5. Thefollowing steps are merely manufacturing method of conventional VDMOSdevices, and therefore will be described less detailedly.

Step 6: form a trench in each N-type pillar 2 a by lithography and etchfor forming a polysilicon gate 6 in the subsequent steps. The trench hasa width of, for example, less than 2 μm.

Step 7: form a silicon dioxide layer on side walls and the bottom ofeach trench formed in step 6 by thermal oxidation. The silicon dioxidelayers serve as gate oxide layers 5, and the gate oxide layers 5 have athickness of, for example, 1000 Å.

A silicon dioxide layer (not shown) is also formed on top surface ofeach P-type pillar 4 during the thermal oxidation process to serve as asilicon protection layer during the subsequent polysilicon etchingprocess. The silicon dioxide layer on top surface of each P-type pillar4 will be partly removed during the polysilicon etching process; itsthickness may also be reduced during some wet etching processes; theremaining silicon dioxide layer may serve as a buffer layer during thesubsequent ion implantation process. The silicon dioxide layer coveringthe contact hole regions will be totally removed in step 12 when etchingcontact holes or be totally removed before step 12.

Step 8: fill each trench formed in step 6 with polysilicon bydeposition, and then remove the polysilicon above the N-type epitaxiallayer 2 by planarization or dry etch process, so as to form apolysilicon gate 6 in each trench formed in step 6.

Step 9: form a P-well 7 above each P-type pillar 4 by lithography andion implantation, wherein, the doping concentration of P-type impurityin the P-well 7 is, for example, from 1×10¹⁷ atoms/cm³ to 9×10¹⁷atoms/cm³; the height of the P-well 7 h3 is, for example, from 1.5 μm to3 μm; the three-dimensional shape of the P-well 7 is the same with theP-type pillars 4 and the N-type pillars 2 a, namely wall-shaped orpillar-shaped. After the formation of the P-wells 7, the height of theP-type pillars 4 and the height of the main bodies 4 a of the P-typepillars 4 is reduced to h1+h2′, and the height of the additionalstructures 4 b is reduced to h2′, wherein h2′=h2−h3.

Step 10: form N-type heavily doped source regions 8 in each P-well 7 byperforming lithography and ion implantation to certain regions of theP-well 7, wherein the doping concentration of N-type impurity in theheavily doped N-type source regions 8 is greater than 1×10²⁰ atoms/cm³.

Step 11: deposit a dielectric layer 9 on the entire substrate, whereinthe dielectric layer 9 has a thickness of, for example, from 5000 Å to10000 Å.

Step 12: form contact holes in the dielectric layer 9 by lithography andetch; each contact hole is located above a P-well 7 and is connected tothe P-well 7.

Step 13: form a P-type heavily doped contact region 11 in the P-well 7under each contact hole, wherein the doping concentration of P-typeimpurity in the P-type heavily doped contact regions 11 is, for example,higher than 1×10¹⁸ atoms/cm³.

Step 14: fill metal into the contact holes by deposition and remove themetal above the dielectric layer 9 by planarization, so as to form acontact hole electrode 10 in each contact hole.

Step 15: deposit a surface metal layer 12 on the entire substrate andpick up a source electrode 21 from the surface metal layer 12; pick up agate electrode 22 from the polysilicon gates 6; the surface metal layer12 has a thickness of, for example, from 10000 Å to 50000 Å.

Step 16: perform backside grinding to the N-type heavily doped substrate1 by, for example, chemical mechanical polishing (CMP), and deposit abackside metal layer 13 on the backside of the N-type heavily dopedsubstrate 1; a drain electrode 23 is picked up from the backside metallayer 13.

In the superjunction structure shown in FIG. 1, a P-type pillar 4 hastwo sections from the top down; in other embodiments, a P-type pillar 4may have more than two sections in the vertical direction as shown inFIG. 5( a) to FIG. 5( c), in which a second section from the top downhas a groove formed in its top, and the groove has a profile wider atthe top and narrower at the bottom (the groove may be of any shape asshown in FIG. 4( a) to FIG. 4( h)); a first section from the top down isformed in the groove and also has a shape wider at the top and narrowerat the bottom; each of the remaining sections of the P-type pillar 4 mayhave a flat top surface or a surface with a groove, which shall not belimited; the bottom surface of an upper section is always matched withthe top surface of a lower section directly under it, that is to say, ifthe top surface of a lower section is flat, the bottom surface of theupper section is also flat; if a groove is formed in the top surface ofa lower section, the bottom surface of the upper section is fully filledin the groove. P-type impurities are evenly doped in each section of aP-type pillar, while the doping concentrations of the respectivesections in a P-type pillar decrease from the top down.

In the manufacturing method of superjunction structure described in step2 to step 5 above, each P-type pillar 4 is divided to two sections,which may only represent as an example. In the cases that a P-typepillar 4 has more than two sections as shown in FIG. 5( a) to FIG. 5(c), the second section from the top down has a groove formed in its top,and the groove has a profile wider at the top and narrower at thebottom; while the first section from the top down is formed in thegroove and also has a profile wider at the top and narrower at thebottom; the rest part of the P-type pillar 4 may be divided into nsections, and the profile of each section is not limited. In such cases,the above step 3 and step 4 will be combined and modified as follows:fill the trenches with P-type silicon by conducting more than two filingsteps from the bottom up, wherein a latter filing step adopts a greaterdoping concentration of the P-type silicon than a former filing step;the P-type silicon filled by the second last filing step in each trenchhas a groove formed in its top, and the groove has a profile wider atthe top and narrower at the bottom; the P-type silicon filled by thelast filing step in each trench is filled in the groove formed by thesecond last filing step. Besides, the above step 5 will be modified asfollows: remove the P-type silicon filled by the second last and thelast filing steps above the surface of the N-type epitaxial layer; theremaining P-type silicon filled by the last filing step in the trenchforms the first section of a P-type pillar and the remaining P-typesilicon filled by the second last filing step in the trench forms asecond section from the top.

The description below will focus on the relationship between the dopingconcentrations in the P-type pillars and the doping concentrations inthe N-type pillars of the superjunction structure of the presentinvention. For the convenience of description, a practical applicationenvironment is given as an example as follows: in a superjunction MOStransistor as shown in FIG. 1, the reverse breakdown voltage of thesuperjunction MOS transistor is 600V; the resistivity of the N-typeheavily doped substrate 1 is from 0.001 Ω·cm to 0.003 Ω·cm; both thewidths of each P-type pillar 4 and each N-type pillar 2 a are 4 μm; thethickness of the N-type epitaxial layer 2 is 45 μm; and the height ofeach P-type pillar 4, h1+h2′, is 35 μm, wherein h1 is 25 μm and h2′ is10 μm.

Example 1

referring to FIG. 3 a, the horizontal axis indicates the height of anN-type pillar 2 a; the horizontal coordinate of zero indicates thelowest position of a P-type pillar 4; the horizontal coordinate of h1indicates the lowest position of the additional structure 4 b in aP-type pillar 4; the horizontal coordinate of h1+h2′ indicates thehighest position of a P-type pillar 4; the doping concentration of theN-type pillar 2 a is represented by the solid line, which shows a linearchange; the doping concentration at the center position in the verticaldirection in the N-type pillar (corresponding to the horizontalcoordinate of (h1+h2′)/2) is Nn0; the doping concentration at the bottomof the N-type pillar is Nn0×130%; and the doping concentration at thetop of the N-type pillar is Nn0×70%; wherein Nn0 is, for example, 3×10¹⁵atoms/cm³.

In this case, the optimal doping concentration Pp0 of the P-type pillar4 is equal to Nn0, wherein Pp0 is defined as the doping concentration ofthe P-type pillar 4 when the P-type pillar 4 is completely evenly doped(i.e., the P-type pillar 4 only has the main body 4 a and does not havethe additional structure 4 b, and the main body 4 a is evenly doped),and the total quantity of P-type impurities in the P-type pillar 4 isequal to the total quantity of N-type impurities in the N-type pillar 2a. The definition of Pp0 remains unchanged throughout the description.

The doping concentrations in a P-type pillar 4 in the superjunctionstructure of the present invention may be selected as follows:

Option 1: the doping concentration of the main body 4 a of the P-typepillar is lower than Pp0, and the doping concentration of the additionalstructure 4 b of the P-type pillar is greater than Pp0. For example,referring to FIG. 3 b, the horizontal axis in FIG. 3 b has the sameindication with that in FIG. 3 a; the doping concentration of the P-typepillar 4 is represented by the solid line; the doping concentration ofthe main body 4 a is Pp0×90%; the doping concentration of the additionalstructure 4 b is Pp0×300%. In a height range of from h1 to h1+h2′, thereal structure of the P-type pillar 4 shall include both a part of themain body 4 a and the additional structure 4 b, however, only the dopingconcentration of the additional structure 4 b is shown in FIG. 3 b, andit is the same in FIG. 3 c and FIG. 3 d.

Option 2: the doping concentration of the main body 4 a of the P-typepillar is equal to Pp0, and the doping concentration of the additionalstructure 4 b of the P-type pillar is greater than Pp0. For example,referring to FIG. 3 c, the horizontal axis in FIG. 3 c has the sameindication with that in FIG. 3 a; the doping concentration of the P-typepillar 4 is represented by the solid line; the doping concentration ofthe main body 4 a is Pp0 and the doping concentration of the additionalstructure 4 b is Pp0×300%.

Option 3: the doping concentration of the main body 4 a of the P-typepillar is greater than Pp0, but lower than the highest dopingconcentration in the N-type pillar 2 a, which is Nn0×130%, and thedoping concentration of the additional structure 4 b of the P-typepillar is greater than Pp0. For example, referring to FIG. 3 d, thehorizontal axis in FIG. 3 d has the same indication with that in FIG. 3a; the doping concentration of the P-type pillar 4 is represented by thesolid line; the doping concentration of the main body 4 a is Pp0×110%and the doping concentration of the additional structure 4 b isPp0×300%.

Example 2

referring to FIG. 3 e, the horizontal axis in FIG. 3 e has the sameindication with that in FIG. 3 a; the doping concentration of the N-typepillar 2 a is represented by the solid line; the doping concentration ofthe N-type pillar 2 a changes linearly in the height range of the P-typepillar 4 excluding the additional structure 4 b (i.e., in the heightrange of from 0 to h1); the doping concentration of the N-type pillar 2a at a position corresponding to the lowest position of the additionalstructure 4 b of the P-type pillar is Nn0; the doping concentration isNn0×130% at the bottom of the N-type pillar 2 a; the N-type pillar 2 ahas a constant doping concentration of Nn0 in the height range of theadditional structure 4 b of the P-type pillar (i.e., in the height rangeof from h1 to h1+h2′); wherein Nn0 is, for example, 3×10¹⁵ atoms/cm³.

In this case, the optimal doping concentration Pp0 of the P-type pillar4 is equal to (h1×1.15+h2′)×Nn0/(h1+h2′), wherein the value 1.15 is theratio of the average doping concentration of the linearly changedportion of the N-type pillar 2 a to Nn0.

The doping concentrations in the P-type pillar 4 in the superjunctionstructure of the present invention may be selected as follows: thedoping concentration of the main body 4 a of the P-type pillar is equalto Pp0, and the doping concentration of the additional structure 4 b ofthe P-type pillar is greater than Pp0. For example, referring to FIG. 3c, the doping concentration of the main body 4 a is Pp0 and the dopingconcentration of the additional structure 4 b is Pp0×300%.

Example 3

referring to FIG. 3 f, the horizontal axis in FIG. 3 f has the sameindication with that in FIG. 3 a; the doping concentration of the N-typepillar 2 a is represented by the solid line; the doping concentration ofthe N-type pillar 2 a changes linearly in the height range of the P-typepillar 4 excluding the additional structure 4 b (i.e., in the heightrange of from 0 to h1); the doping concentration of the N-type pillar 2a at a position corresponding to the lowest position of the additionalstructure 4 b of the P-type pillar is Nn0; the doping concentration isNn0×130% at the bottom of the N-type pillar 2 a; the N-type pillar 2 ahas a constant doping concentration of Nn0×80% in the height range ofthe additional structure 4 b of the P-type pillar (i.e., in the heightrange of from h1 to h1+h2′); wherein Nn0 is equal to, for example,3×10¹⁵ atoms/cm³.

In this case, the optimal doping concentration of the P-type pillar 4Pp0 is equal to (h1×1.15+h2′×0.8)×Nn0/(h1+h2′), wherein the value 1.15is the ratio of the average doping concentration of the linearly changedportion of the N-type pillar 2 a to Nn0.

The doping concentrations in the P-type pillar 4 in the superjunctionstructure of the present invention may be selected as follows: thedoping concentration of the main body 4 a of the P-type pillar is equalto Pp0, and the doping concentration of the additional structure 4 b ofthe P-type pillar is higher than Pp0. For example, referring to FIG. 3c, the doping concentration of the main body 4 a is Pp0 and the dopingconcentration of the additional structure 4 b is Pp0×300%.

The above embodiments are provided for the purpose of describing theinvention and are not intended to limit the scope of the invention inany way. It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Thus, it is intended that the presentinvention covers the modifications and variations of this invention.

What is claimed is:
 1. A superjunction structure, comprising afirst-type epitaxial layer and a plurality of second-type pillars formedtherein, a part of the first-type epitaxial layer between each twoadjacent second-type pillars serving as a first-type pillar, so as toform alternately arranged first-type pillars and second-type pillars,wherein: each second-type pillar consists of at least two sections in avertical direction, a second section from the top down having a grooveformed in its top, the groove having a profile wider at the top andnarrower at the bottom, a first section from the top down being formedin the groove and also having a profile wider at the top and narrower atthe bottom; each section of the second-type pillar includes a secondtype impurity, doping concentrations of the second type impurity in therespective sections decreasing from the top down; each first-type pillarincludes first-type impurities distributed in the vertical direction, adoping concentration of the first-type impurities in a lower portion ofthe first-type pillar being greater than or equal to a dopingconcentration of the first-type impurities in an upper portion of thefirst-type pillar; in a bottom of the first-type epitaxial layer, atotal quantity of the second-type impurity in the second-type pillars isless than a total quantity of the first-type impurities in thefirst-type pillars; in a top of the first-type epitaxial layer, a totalquantity of the second-type impurity in the second-type pillars isgreater than a total quantity of the first-type impurities in thefirst-type pillars, further wherein, the first-type is N-type and thesecond-type is P-type, or the first-type is P-type and the second-typeis N-type.
 2. The superjunction structure according to claim 1, wherein:in each second-type pillar, the first section from the top down forms anadditional structure of the second-type pillar, and remaining sectionsof the second-type pillar form a main body of the second-type pillar; adistance between a bottom of the main body and a bottom of theadditional structure is from 25 μm to 30 μm, and a height of theadditional structure is from 2 μm to 8 μm.
 3. The superjunctionstructure according to claim 2, wherein in each second-type pillar, adoping concentration of the second type impurity in the main body islower than or equal to an even doping concentration of the second-typepillar, while a doping concentration of the second type impurity in theadditional structure is greater than the even doping concentration ofthe second-type pillar, further wherein the even doping concentration ofthe second-type pillar is defined as a doping concentration of thesecond-type pillar measured when the second-type pillar is evenly dopedwith the second-type impurity and a total quantity of the second-typeimpurity in the second-type pillar is equal to a total quantity of thefirst-type impurities in a first-type pillar.
 4. The superjunctionstructure according to claim 3, wherein the doping concentration of thesecond type impurity in the main body is 0.5˜1 time of the even dopingconcentration of the second-type pillar, and the doping concentration ofthe second type impurity in the additional structure is 3˜10 times ofthe even doping concentration of the second-type pillar.
 5. Thesuperjunction structure according to claim 2, wherein in eachsecond-type pillar, a doping concentration of the second type impurityin the main body is greater than an even doping concentration of thesecond-type pillar but lower than a maximum doping concentration withinthe first-type pillar, while a doping concentration of the second typeimpurity in the additional structure is greater than the even dopingconcentration of the second-type pillar, further wherein the even dopingconcentration of the second-type pillar is defined as a dopingconcentration of the second-type pillar measured when the second-typepillar is evenly doped with the second-type impurity and a totalquantity of the second-type impurity in the second-type pillar is equalto a total quantity of the first-type impurities in a first-type pillar.6. A method of manufacturing the superjunction structure according toclaim 1, comprising: providing a first-type epitaxial layer and forminga plurality of trenches in the first-type epitaxial layer by etch,wherein a doping concentration in a lower portion of the first-typeepitaxial layer is greater than or equal to a doping concentration in anupper portion of the first-type epitaxial layer; filling the trencheswith a second-type silicon by conducting at least two filing steps fromthe bottom up, each latter filing step adopting a greater dopingconcentration of the second-type silicon than its former filing step,wherein the second-type silicon filled by the second last filing step ineach trench has a groove formed in its top, the groove having a profilewider at the top and narrower at the bottom, the second-type siliconfilled by the last filing step in each trench being formed in thegroove; and removing the second-type silicon above a surface of thefirst-type epitaxial layer.
 7. A superjunction MOS transistor,comprising: a first-type heavily doped substrate; a first-type epitaxiallayer formed on the first-type heavily doped substrate; and a pluralityof second-type pillars formed in the first-type epitaxial layer,wherein: a part of the first-type epitaxial layer between each twoadjacent second-type pillars serves as a first-type pillar, so as toform alternately arranged first-type pillars and second-type pillars;each second-type pillar consists of at least two sections in a verticaldirection, a second section from the top down having a groove formed inits top, the groove having a profile wider at the top and narrower atthe bottom, a first section from the top down being formed in the grooveand also having a profile wider at the top and narrower at the bottom;each section of the second-type pillar includes a second type impurity,doping concentrations of the second type impurity in the respectivesections decreasing from the top down; each first-type pillar includesfirst-type impurities distributed in the vertical direction, a dopingconcentration of the first-type impurities in a lower portion of thefirst-type pillar being greater than or equal to a doping concentrationof the first-type impurities in an upper portion of the first-typepillar, further wherein, the first-type is N-type and the second-type isP-type, or the first-type is P-type and the second-type is N-type. 8.The superjunction MOS transistor according to claim 7, wherein in eachsecond-type pillar, the first section from the top down forms anadditional structure of the second-type pillar, and remaining sectionsof the second-type pillar form a main body of the second-type pillar; adistance between a bottom of the main body and a bottom of theadditional structure is from 25 μm to 30 μm; and a height of theadditional structure is from 2 μm to 8 μm.
 9. The superjunction MOStransistor according to claim 8, wherein in each second-type pillar, adoping concentration of the second type impurity in the main body islower than or equal to an even doping concentration of the second-typepillar, while a doping concentration of the second type impurity in theadditional structure is greater than the even doping concentration ofthe second-type pillar, further wherein the even doping concentration ofthe second-type pillar is defined as a doping concentration of thesecond-type pillar measured when the second-type pillar is evenly dopedwith the second-type impurity and a total quantity of the second-typeimpurity in the second-type pillar is equal to a total quantity of thefirst-type impurities in a first-type pillar.
 10. The superjunction MOStransistor according to claim 9, wherein the doping concentration of thesecond type impurity in the main body is 0.5˜1 time of the even dopingconcentration of the second-type pillar, and the doping concentration ofthe second type impurity in the additional structure is 3˜10 times ofthe even doping concentration of the second-type pillar.
 11. Thesuperjunction MOS transistor according to claim 8, wherein in eachsecond-type pillar, a doping concentration of the second type impurityin the main body is greater than an even doping concentration of thesecond-type pillar but lower than a maximum doping concentration withinthe first-type pillar, while a doping concentration of the second typeimpurity in the additional structure is greater than the even dopingconcentration of the second-type pillar, further wherein the even dopingconcentration of the second-type pillar is defined as a dopingconcentration of the second-type pillar measured when the second-typepillar is evenly doped with the second-type impurity and a totalquantity of the second-type impurity in the second-type pillar is equalto a total quantity of the first-type impurities in a first-type pillar.12. The superjunction MOS transistor according to claim 7, furthercomprising: gate oxide layers of bowl-shapes, each being in contact witha top of a first-type pillar; polysilicon gates, each being surroundedby a gate oxide layer; second-type wells, each being in contact with atop of a second-type pillar and parts of the tops of the first-typepillars adjacent to the second-type pillar; first-type heavily dopedsource regions and second-type heavily doped contact regions, formedunder surfaces of the second-type wells; a dielectric layer, formedabove the gate oxide layers and the polysilicon gates; contact holeelectrodes, formed above the first-type heavily doped source regions andthe second-type heavily doped contact regions; a surface metal layer,formed on the dielectric layer and the contact hole electrodes; a sourceelectrode, picked up from the surface metal layer; gate electrodes,picked up from the polysilicon gates; a backside metal layer, formed ona backside of the first-type heavily doped substrate; and a drainelectrode, picked up from the backside metal layer.